(a) Field of the Invention
The present invention relates to a power-down control method of a fuel cell hybrid electric vehicle (FC-HEV). More particularly, the present invention relates to a power-down control method of a fuel cell-super capacitor hybrid electric vehicle that can safely power down high voltage parts by optimally controlling the order in which elements of the fuel cell system are turned off during key-off.
(b) Background Art
A typical fuel cell oxidizes a hydrogen-containing fuel such as liquefied natural gas (LNG), liquefied petroleum gas (LPG), methanol, etc, and converts the chemical energy produced during the reaction to electric energy.
If a fuel cell is used as the only power source of an electric vehicle, the fuel cell powers all loads of the vehicle, which decreases the efficiency of the fuel cell.
Moreover, voltage required by a driving motor cannot be supplied since output voltage is rapidly reduced at high speeds, which decreases the acceleration performance of the vehicle.
Furthermore, if a sudden load is applied to the vehicle, the output voltage of the fuel cell drops momentarily and thereby sufficient power is not supplied to the driving motor, thus deteriorating vehicle performance.
In addition, since the fuel cell has unidirectional output characteristics, it is impossible to recover energy from the driving motor while braking the vehicle, thus deteriorating the efficiency of the vehicle system.
In an attempt to solve such problems, a fuel cell-battery hybrid, or fuel cell-super capacitor hybrid system has been developed. Such a system includes a high voltage battery or a super capacitor in addition to the fuel cell.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art that is already known to a person skilled in the art.